1. Field of the Invention
This invention relates to a method and apparatus for gapping a slide fastener chain or removing a group of slide fastener elements from selected areas along a continuous length of slide fastener chain to provide "element-free gaps", the spacing between adjacent "gaps" largely determining the length of an individual finished slide fastener product.
2. Prior Art
Various methods and apparatus for gapping slide fasteners have been proposed heretofore. A typical example of the prior art methods and apparatus usually involves cutting the coupling head portions of the fastener elements and removing the cut pieces from the fastener tapes to leave gaps thereat free of fastener elements. To this end, the confronting, abutted edges of the tapes are required to be forced apart from each other widely enough to permit a punch to move therethrough. However, due to the tendency of the fastener tapes to resist the forcing apart or spreading open of their opposed element-carrying edges which have been brought into abutting engagement with each other, those portions of the tapes which lie between the locations of gaps to be formed and the withdrawal rollers disposed to guide the fastener chain out of the system, are prone to become elongated or stretched out. It has therefore been necessary, when predetermining the inter-gap spacing or intervals, to take into account such potential errors which may arise out of the elongation or stretching of the tapes. What makes this problem more complex is the fact that the material of the fastener tapes varies, it being a naturally occuring fiber in some instances or synthetic fibers in other instances, depending upon the garment or other articles to which the fastener is applied, or that the physical properties of the tapes also vary with whether they are woven or knitted, with the results that the rate of elongation of the tape under tensile force is variable with such varying conditions. Tape elongation is further subject to change with how rows of fastener elements are sewn to the support tapes, or even with the environmental conditions of the manufacture of fasteners. With conventional methods and apparatus, it has been difficult to determine the positions of "gaps" to be formed with reasonable accuracy, and it has been furthermore required to re-calibrate the equipment when the type of fastener chain changes.